A disoriented pilot was so tired that he sent his passenger plane into a sudden 400ft nosedive because he mistook the planet Venus for an oncoming aircraft.
The incident, which occurred on a Boeing 757 Air Canada flight between Toronto and Zurich, caused injuries to 16 people on board, many of whom had to be hospitalised.
A report on the incident has been released by the Transportation Safety Board of Canada. It reveals that the plane's first officer had been taking a scheduled nap when he awoke and suddenly slammed the plane into a nosedive.
The officer had been awoken by the captain's report on their flight position. Cockpit alerts had been going off because a US Airforce plane was approaching 300 yards below. The captain was aware of this, but the "confused and disoriented" first officer mistook Venus for the approaching plane, and, thinking it was coming straight at him, overrode the autopilot and sent the jet into a sharp nosedive.
Most of the 103 passengers onboard were sleeping at the time and were wearing seat belts, but 14 passengers and two flight attendants were thrown around the aircraft, suffering cuts and bruises.
Louisa Pickering, a passenger on the flight, told the BBC she as asleep when she was thrown out of her window seat and slammed into the ceiling.
"I hit the top of the ceiling and and fell back to the ground," she said. After that it was kind of chaos."
After falling 440feet, the captain managed to regain control of the plane and returned it to its cruising altitude, and the military aircraft passed safely underneath.
The report concluded that the first officer, who had been asleep for 75 minutes, was suffering "sleep inertia magnified by fatigue". It also said that the flight crews were not following standard procedures for "strategic napping" (normally 40 minutes). Pilots are supposed to have 15 minutes after a nap to allow them to awaken fully before taking control.
The incident has again highlighted the subject of passenger safety in the light of pilot fatigue. A recent study from the British Airline Pilots Association (BALPA) found that one in five pilots felt that their ability fo fly an aeroplane was compromised more than once a week.
The Association says that fatigue among pilots is a growing problem and that tiredness now accounts for between 15 and 20 per cent of accidents. At the same time, the EU is imposing increased flying hours.
The Air Canada Pilots Association has called for a mandate for a third pilot on eastbound transatlantic flights. However Air Canada says it has already taken steps to allow pilots who are too tired to fly to withdraw from assignments.
British pilot falls asleep at the controls
Air traffic controllers should sleep on the job, say experts
Sign up to our weekly newsletterFollow us on TwitterBecome a fan on Facebook